1. Technical Field
An embodiment of the invention relates to an outboard motor, particularly to an outboard motor that can prevent a throttle valve of a mounted engine from being frozen (iced) and stuck.
2. Background Art
Conventionally, there is widely known an outboard motor in which an inlet of an air intake passage of a mounted engine is positioned at interior space of an engine cover to suck air in the interior space to operate the engine. In such a configuration, since air warmed through, for instance, heat generated by the engine enters the air intake passage, charging efficiency of the engine is degraded and therefore, it leads to disadvantages such as the decrease in the engine output.
To cope with it, an outboard motor having an air intake passage that opens at an engine cover to directly suck external air of lower in temperature than air of internal space, is proposed so as to increase the charging efficiency to improve the engine output, as taught, for example, by Japanese Laid-Open Patent Application No. 2008-88881 ('881). However, in '881, when the outside air temperature is relatively low so that the temperature of sucked air passing through a throttle valve of the air intake passage drops below zero, moisture in the air is frozen (iced) and it may make the throttle valve stuck.
One measure to deal with it is proposed in Japanese Laid-Open Patent Application No. Hei 10(1998)-331621 ('621), in which a flow passage is installed near a throttle valve and a coolant warmed by exhaust heat of an engine is flown therethrough, whereby the throttle valve (more precisely, a throttle body) is warmed, thereby preventing the throttle valve from being frozen (iced) and stuck.